Plunger operated locks are typically used to secure utility electric meters. A plunger operated lock arrangement is disclosed in U.S. Pat. No. 4,254,647 for example. Here the lock is used to secure a box in which an electric utility meter is enclosed. The plunger may be of any commercially available construction and may be, for example, of the type disclosed in U.S. Pat. No. 4,015,456. Other types of plunger locks are also available such as disclosed in U.S. Pat. No. 3,186,196 referred to in the U.S. Pat. No. 4,015,456 patent.
A so called key is required to operate these locks. For example reference is made to U.S. Pat. No. 4,296,616 and also to the '196 patent referenced above. In the plunger, a pin is biased away from a housing opening to a lock position and may be pulled to the unlock position. The pin is pulled by the so called key to the unlocked state. The key comprises an operating rod having an enlarged head which serves as a cam. The head and rod are within a sleeve formed into resilient segments or jaws. The enlarged head operates the jaws to expand them, the jaws having a quiescent state in which they are contracted. The jaws are inserted in the plunger lock and expanded to grab the pin therein to place the lock in its unlock state.
The keys comprise a mechanism within a housing and whose parts for operating the enlarged head and jaws are secured together in a manner such that factory disassembly is required. For example the jaws and head are part of a cartridge, which with springs, are inserted in a housing whose parts are staked together such that tools are required to disassemble the housing. Further, a handle coupled to the head operating rod is pinned to a shaft of the cartridge such that tools are required to disassemble this pinned arrangement. The repetitive operation of the head and jaws wears out the head and jaws so that the key periodically requires replacement. This requires the utility or other owner of the key and plunger locks to periodically return the key to the factory for repair. As a result, extra keys are required by the user which is costly and also the keys tend to be used until inoperative which is a nuisance.